Employment diverse or dependent upon a single employer?

Im somewhat new to BP but am trying to quickly ramp up on my understanding across a very diverse set of topics so when I purchase my first small multi units I don't embarrass myself too horribly haha.  

Landlord friendly, large diverse employers, good price to rent ratios.

Diverse resident employment profile at a property (meaning do many property residents work for one major employer or are there many employers) 4.

There is some good protection here.Also, the economy of NYC is very diverse and I would say its safe to say that it will be a high demand city for many years to come.  

Rentals are one way, and yes you would need a few to replace the average wage.The more you network, the more diverse opportunities you will find.

You'll have better appreciation spread out through multiple buildings, little more more security with a bigger number of tenants, better depreciation (infact i think you have to gain some leverage to actually take advantage of that) and if you're in different markets it helps so you have some diversity with how your properites appreciate.

Is the economy diverse?

It is extremely diverse so understanding the demographics of areas and flows is extremely important IMO. 

People will always want to live in these places which are a melting pot with diverse population, younger crowd, job opportunities and indescribable energy.